This invention relates to a bag having an oxygen absorbent, characterized in that at least part of the material constituting the bag is composed of a microporous film having a plurality of fine openings, and a gas permeable sheet.
In order to preserve foodstuffs, it is necessary to prevent the foodstuffs from getting moldy and from putrefying. In the prior art methods, the gas present in the inner part of a content-charged container was replaced by an inert gas or the container was sterilized. However, replacement of oxygen by an inert gas requires large-scale apparatus and sterilization of the filled container may cause change in quality of the contents. Additives, such as antioxidant, have been used for preserving foodstuffs. However, recently, governments have started to regulate the use of additives for foods, since some additives have been found to be injurious to humans.
Molds or eumycetes, bacteria and higher organisms such as insects tend to disturb preservation of foodstuffs. These mold eumycetes, bacteria and insects live and grow in the presence of oxygen and cause putrefaction and change in quality of foodstuffs.
Therefore, if oxygen can be selectively removed from the empty space of the filled container, the problems of putrefaction and change in quality of foodstuffs can be overcome, and it will become possible to preserve foodstuffs a long time.
A bag having an oxygen absorbent in which at least part of the material constituting the bag is composed of a microporous film was described in U.S. Ser. No. 119,876 filed on Feb. 8, 1980 and now abandoned, assigned to the assignee of this invention.
However a microporous film is mono-layer film, so it is difficult to heat-seal the microporous film by means of conventional packaging machines. The reason is that when two sheets of mono-layer films are adhered by melting an inside portion of the mono-layer film, melted film is adhered to heat-seal bars or heat rolls of the machine. A special heat-sealer, such as impulse heat-sealer, is necessary in order to heat-seal mono-layer film. When such a special heat sealer is used in an automatic packaging machine in order to heat-seal the mono-layer film, it is impossible to operate the automatic packaging machine at a high speed. So, when the mono-layer film is heat-sealed by impulse heat sealer, a decrease in efficiency is unavoidable. In addition, the microporous film is weakened. So a microporous film is not practical as a packaging material for packing an oxygen absorbent.